British & Irish Botany 3(1): 1-32, 2021 Survey of the nothogenus ×Elyhordeum, with the description of a new nothospecies Michael P. Wilcox1*; Stuart D. Desjardins2; Clive A. Stace3 1 Bradford, UK; 2 Department of Genetics and Genome Biology, University of Leicester, UK; 3 Middlewood Green, Suffolk, UK *Corresponding author: Michael P. Wilcox: [email protected] This pdf constitutes the Version of Record published on 16th February 2021 Abstract The occurrences in Denmark, Britain and Ireland of ×Elyhordeum langei (Elymus repens × Hordeum secalinum) are documented, and the variation in this hybrid is described. The French hybrid ×E. rouxii is also briefly covered. The discovery, distribution and characters of a new hybrid, E. caninus × H. secalinum, first found in North Lincolnshire, England, in 2014, are described and discussed. Cytological and molecular studies are included. The latter is described as ×E. kirbyi M.P.Wilcox, hybr. nov. Keywords: Elymus, Hordeum; intergeneric hybrid; ITS sequencing; chromosome number; unreduced gametes; chloroplast DNA. Introduction Poaceae tribe Triticeae Dumort. (syn. Hordeeae) has been recognised in more or less its present circumscription for many years (Hubbard, 1948; Soreng et al., 2017); in the past 70 years it has not been subject to the multiple rearrangements that have beset many other tribes, notably the Poeae (syn. Festuceae). It contains the important cereals wheat (Triticum L.), barley (Hordeum L.) and rye (Secale L.), as well as the wild grasses variously known as wheatgrasses or couchgrasses that have until quite recently been mainly placed in the genus Agropyron Gaertn. This paper concerns natural intergeneric hybrids between Hordeum and the couchgrasses. In the British literature our four species of couchgrass were retained in Agropyron until Melderis (1978) segregated them into the genus Elymus L. Two of the species, E. repens (L.) Gould (Common Couch) (Figs. 1A-C) and E. caninus (L.) L. (Bearded Couch) (Fig. 1D) have retained their specific epithets during several taxonomic realignments, but the other two have accumulated multiple synonyms, partly due to the rules of nomenclature and partly because of changing taxonomic opinions. The Sea Couch was known as Agropyron pungens (Pers.) Roem. & Schult. by Hubbard (1954) and Tutin (1962), Elymus pycnanthus (Godron) Melderis by Melderis (1978), Elytrigia atherica (Link) Kerguélen by Stace (2010) and Stace et al. (2015), Elytrigia acuta (DC.) Tzvelev by Tison & de Foucault (2014), Thinopyrum acutum (DC.) Banfi by Banfi (2018), and Elymus athericus (Link) Kerguélen by Cope & Gray (2009), Stace (2019) and Duistermaat (2020). The classification of the fourth species, Sand Couch, is complicated by the fact that there has been disagreement as 1 to whether the Mediterranean hexaploid and Atlantic tetraploid populations should be placed in the same species (as separate subspecies) or treated as separate species. Our taxon, the tetraploid, was known as Agropyron junceiforme (Á. & D. Löve) Á. & D. Löve by Hubbard (1954) and Tutin (1962), Elymus farctus (Viv.) Runemark ex Melderis subsp. boreali-atlanticus (Simonet & Guin.) Melderis by Melderis (1978), Cope & Gray (2009) and Duistermaat (2020), Elytrigia juncea (L.) Nevski subsp. boreoatlantica (Simonet & Guin.) Hyl. by Stace (2010), Tison & de Foucault (2014) and Stace et al. (2015), Thinopyrum junceiforme (Á. & D. Löve) Á. Löve by Banfi (2018), and Elymus junceiformis (Á. & D. Löve) Hand & Buttler by Stace (2019). It is of course important to understand such a wide range of opinions when consulting the extensive literature, but an appraisal of their relative merits is not relevant here. Nor do the numerous wild interspecific hybrids within the genus Elymus concern the present study. To simplify matters for present purposes we recognise the two chromosome races (Mediterranean and Atlantic) of the Sand Couch as separate species, and place all four British species of couchgrass in the genus Elymus as E. caninus, E. repens, E. athericus and E. junceiformis. The Mediterranean hexaploid Sand Couch is to be known as E. farctus. The cytological and morphological distinctions between E. farctus and E. junceiformis were detailed by Simonet (1935a,b). Figure 1. Inflorescences. A, Elymus repens f. repens lateral view, photo Richard Stace; B. Elymus repens f. repens abaxial view, photo Richard Stace; C. E. repens f. aristatus; D. E. caninus; E, Hordeum secalinum. 2 Nothogenera involving hybrids between Hordeum and couchgrasses Hybrids between Hordeum and Elymus fall under the nothogeneric name ×Elyhordeum Mansf. ex Tsitsin & K.A. Petrova (1955). There is a later synonym ×Elymordeum Lepage (1957) (see under Taxonomic Conclusions). In addition there is a range of other nothogeneric names available to cater for treatments in which one or more of our four couchgrasses are placed in genera other than Elymus, and one catering for a split of Hordeum: Triticum × Hordeum = ×Tritordeum Asch. & Graebn., Syn. Mitteleur. Fl. 2, Abth. 1: 748 (1902) Agropyron × Hordeum = ×Agrohordeum E.G. Camus ex A. Camus, Bull. Mus. Natl. Hist. Nat. 33: 537 (1927) Synonyms: ×Agropyrohordeum E.G. Camus ex A. Camus, Rivièra Sci. 21: 44 (1934) ×Agropyrhordeum P. Fourn., Quatre Fl. France 91 (1935) ×Hordeopyron Simonet, Compt. Rend. Hebd. Séances Acad. Sci. 201: 1212 (1935a) Elytrigia Desv. × Hordeum = ×Elytrordeum Hyl., Bot. Not. 1953: 357 (1953) Roegneria K. Koch x Hordeum = ×Horderoegneria Tzvelev, Fl. Arct. URSS 2: 241 (1964) Sitanion Raf. ×Hordeum = ×Sitordeum Bowden, Canad. J. Bot. 45: 722 (1967) Elymus × Critesion Raf. = ×Elytesion Barkworth & D.R. Dewey, Amer. J. Bot. 72: 772 (1985) The genus Hordelymus (Jess.) Jess. ex Harz, Landw. Samenk. 2: 1147 (1885) should also be mentioned. This is not a nothogenus but a genus containing sexual non-hybrid species. However, the same name was coined as a nothogenus, ×Hordelymus Bachteev & Darevsk., Bot. Zhurn. (Moscow & Leningrad) 35: 191 (1950). This predates x Elyhordeum but is illegitimate (later homonym). Another genus to note is Rouxia Husn., Gram. Fr. Belg. 76 (1899), which was created to accommodate Agropyron rouxii Gren. & Duval-Jouve as R. hordeoides Husn. This is not a nothogenus, but it was later wrongly treated as one to replace ×Agrohordeum by Kerguélen (1975), who made the combination ×Rouxia rouxii (Gren. & Duval-Jouve) Kerguélen. As stated above, for present purposes we are placing all our four couchgrasses under Elymus, so all intergeneric hybrids with Hordeum come under ×Elyhordeum. Discovery and distribution of ×Elyhordeum taxa in western Europe Two hybrids have been reported previously and a further one has recently been discovered in North Lincolnshire, all involving Hordeum secalinum Schreb. (Fig. 1E) as one parent. E. repens × H. secalinum = ×Elyhordeum langei (K. Richt.) Melderis ×Elyhordeum langei was discovered in July 1865 by Nielsen (1872) at Stubberup on the island of Sjælland (Zealand) in Denmark (Fig. 2), where it was known from 1865 to 1877. It was first recorded by Nielsen as Agropyron repens var. hordeacea, but his brief note did mention the possibility of its being a hybrid with Hordeum secalinum. This parentage was formally adopted by Lange (1886), but he did not give it a binomial. Nevertheless Richter (1890) described it as Agropyron × langei, and it was later authors who transferred it to nothogeneric status. The morphology 3 of this hybrid was described in some detail by Vestergren (1925), without commenting on its nomenclature. Hansen (1960) mentioned it briefly in a survey of Danish Elytrigia hybrids, but shortly after (Hansen, 1965) reported a second site at Marstal on the small island of Ærøs, about 70 km from the first locality. There are records from there between 1961 and 1964, but it might have persisted longer. Hansen (d. 2008) told Henry Nielsen that the Ærøs population died out "about 30 years ago"; some was transplanted to the Copenhagen Botanic Garden (Hansen, 1965) but this also died out (Jens Christian Schou, pers. Comm., 2020). Figure 2. Lectotype of ×Elyhordeum langei (C10021863), reproduced with permission from Københavns Universitet Herbarium (C). 4 ×Elyhordeum langei was discovered in the British Isles in 1945 by Mrs C.I. Sandwith (Hubbard & Sandwith, 1955a, 1955b) at Shirehampton, West Gloucestershire, where it was known until 1954, but there are no records since then, despite searches. In the past three decades other localities for this hybrid have been reported from West Gloucestershire, mostly by C. & M.A.R. Kitchen: (a) in an semi-continuous zone along a c. 2 km stretch of the east bank of the lower reaches of the R. Severn south of Aust, at Northwick Warth, between Old Passage and just north-east of New Passage, ST552870 to ST563888 (first record made in 1991 by S. O'Donnell) (Fig. 3A). Figure 3. Natural stands of ×Elyhordeum langei. A. Aust, W. Gloucs, with (left to right) Olga Krylova, Clive Lovatt and Clare Kitchen (Mark Kitchen); B. Tewkesbury, E. Gloucs (Clive Lovatt). 5 (b) south of Lydney, in at least three separate stands on the west bank of the R. Severn about 14 km north of the other stands, from Lydney Harbour to Aylburton Warth, ST62189999 to SO64430123 (first record made in 1993 by C. & M.A.R. Kitchen). The hybrid has been confirmed in both areas by C. & M.A.R. Kitchen and C.M. Lovatt in 2020. Elsewhere, confirmed records, which are all still extant, have been made by I.P. Green in 1990 at Alstone, North Somerset, ST310473; by S. Reynolds in 1990 at Ringmoylan, Co. Limerick, R405577; and by C.R. Pope & E.J. Clement in 2015 at Sandown Levels, Isle of Wight, SZ608852. All the above records of ×E. langei, in all four vice-counties, are maritime or estuarine, with definite or possible saline influence at least in the past. However, in July 2020 C.M. Lovatt discovered a fifth locality: two sizeable patches of the hybrid in rough grassland in Tewkesbury Nature Reserve close to the centre of Tewkesbury, East Gloucestershire, SO898323, which is very far from any salinity (Fig. 3B). There are many other records of this hybrid from Britain, from localities as far north as Orkney, and many of them inland, but we cannot confirm that any of them are correctly identified.